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2: The Demography of Blind and Visually Impaired Pedestrians
Pages 10-25

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From page 10...
... This chapter reviews the definitions of visual impairment that are used for purposes of demographic analysis, reports findings from available statistics about the number and characteristics of the visually impaired population, and describes what is known about the patterns of use of travel aids today. The chapter concludes with recommendations for further work to improve our understanding of demographic characteristics relevant to the mobility needs of visually impaired and blind people.
From page 11...
... DEMOGRAPH I C CHARACTER I S T I C S It is possible to estimate the number of legally blind people -- the prevalence of blindness -- in the United States today using the Bureau of the Census projections of the population and the estimated prevalence rates. The prevalence rates published in Vision Problems in the United States (National Society to Prevent Blindness, 1980)
From page 12...
... 12 lo lo lo N US a, U]
From page 13...
... Therefore it is important to examine the characteristics of the legally blind population that might be useful in making inferences about disability: age, age at onset, degree of impairment, other impairments, and social factors. Age The number of cases of blindness for different age categories can be calculated by multiplying the prevalence rate times the population count for each age category.
From page 14...
... _ ~ 0~4 5-19 20~44 45~64 65-74 75-84 85+ AGE CATEGORIES FIGURE 1 Distribution of legal blindness in the general population by age group, 1985e 12 10 Zii~ O o F zg 8 C)
From page 15...
... The usual classifications distinguish between those who are blind from birth or at less than five years of age -- congenital blindness -- and those who have lost sight at older ages -- adventitious blindness. The key to this distinction is the role that early visual experience plays in establishing spatial concepts and visual memories, which later aid functioning when visual impairments reduce or eliminate the ability to see.
From page 16...
... 0-5 5-19 20-44 45-64 65-74 75-84 85+ Total I nf ectious diseases 200 100 200 250 50 50 Injuries/ poisonings 200 350 Neoplasms 100 150 General diseases 50 100 1,050 Prenatal influence 800 2, 250 Unknown or 150 650 unspecif fed Multiple etiologies Total As Percentage of Population: -- 850 500 400 100 50 50 1, 650 100 100 -a - 450 4,700 4,300 6,700 3,900 20,800 1,500 1,150 300 1,750 3,600 2,550 -- 50 100 1,500 3,650 5,200 200 -- 6,200 3,000 1,150 15,850 650 850 1,350 800 3,800 10,850 8,150 11,350 5,900 46,600 .01 .01 .01 .02 .05 .16 .27 .02 SOURCE: National Society to Prevent Blindness { 1980)
From page 17...
... The rate of both prevalence and incidence increase for all impairment categories with age. Roughly 20 percent of the legally blind could be categorized as having "no useful vision" (by adding together the categories of "total blindness" and 2Levels of blindness and visual impairment have been proposed for planning individual rehabilitation programs, travel capability, legal status, tax exemption, supplemental social security awards, and the like: I
From page 18...
... The types and significance of such impairments range widely: mental retardation, affecting the ability to learn how to use an aid; emotional illness, which may affect the motivation to use an aid; orthopedic impairments, which limit ambulation directly; hearing impairments, which limit the use of some types of aids; and other health conditions, such as heart disease, which can result in weakness or pain. All these conditions
From page 19...
... The latter effects occur because social groups have differential access to resources, and/or social norms make certain tasks more important; cultural influences may also make certain types of mobility aids unacceptable. Several national studies, which differ in the ways they identify the population with visual loss (and therefore use different estimated prevalence rates)
From page 20...
... A variety of ETA s has been developed, including sound echo ranging devices, reflected light ranging devices, a computer vision system that speaks messages to the blind traveler, and a dog guide robot. ETAs can be roughly classified using a two-way classification scheme, illustrated in Figure 3.
From page 21...
... The boundaries of the classification scheme are not sharp; some of the devices categorized actually straddle the boundaries or have aspects that fit into more than one category. This is especially true of the signal processing that goes on in the device, since few if any devices simply transduce environmental information.
From page 22...
... The methods used for gathering data include mail questionnaires, phone questionnaires, direct observation, and personal interview. The length of time the visually impaired person had the device ranged from a few months to about 11 years.
From page 23...
... For a survey of this type to yield broadly useful data, comparison groups should be sampled from among the users of dog guides and long canes; it is very likely that these groups overlap. The study should be designed to estimate the probabilities of multiple device use (e.g., Sonicguide and dog guide)
From page 24...
... A Normative Data Base RECOMMENDATION- There is an urgent need for a normative data base that contains information about the entire population of visually impaired and blind people. It should be possible, among other things, to interrogate this data base for information about personal data that indicate readiness for various sensory aids and how sensory readiness changes as a function of maturation and development, from infancy to old age.
From page 25...
... Study of Multiple Impairments On the basis of national studies, we found that more than 50 percent of the severely visually impaired population has at least one additional impairment. RECOMMENDATION: We recommend that an intensive study be conducted on the interaction of visual impairments with other cognitive, sensory, and physical impairments and their effect on mobility problems.


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